Jumping out of gear

[Slartifartfast]

My Alfa164 box keeps jumping out of second when driven 'spiritedly'. This is annoying. It only leaves one hand to do everything else. It has in the past suffered one incident where it ended up in second gear with the selector in neutral as a result of an off. It was coaxed back into neutral by a magnet applied to the end of the rod pulling the gears.
The inside of a gearbox is a bit of a mystery to me. What might make it do that? Since the car is in the infirmary for a while, it can be more easily addressed. I've adjusted the linkage and it's still doing it.

[Mr2Mike]

In this case quite possibly a bent selector which isn't fully engaging the synchro hub into the gear.

[Stan Weiss]

I have had this problem with a BW T-10 4 speed. It that case I replace a warn 1-2 synchro assembly and it fixed the problem.

Stan